Agaricus blazei Murill belonging to the genus Agaricus and also called himemaitsutake mushroom is a kind of mushrooms that grows wild mainly in the mountainous region of the southeastern Brazil, Sao Paulo. The natives have long been using Agaricus blazei Murill as an edible mushroom.
In these years, Agaricus blazei Murill has become widely cultured also in Japan to make its extracts available for the treatment of diabetes and hypertension.
Various investigations have been made to explore substances having an antitumor activity. It is reported that polysaccharides with an antitumor activity are obtained, for example, by extracting the fruit body or mycelium of Agaricus blazei Murill with an aqueous medium (Japanese Patent KOKAI (Laid-Open) Nos. 55-74797, 64-67194, 64-67195, 55-108292, etc.). It is also reported that a nucleic acid component having an antitumor activity is extracted from the fruit body of himematsutake mushroom (Japanese Patent KOKAI (Laid-Open) No. 64-66127). These substances having an antitumor activity are all extracted from the components soluble in an aqueous medium or soluble in hot water.
On the other hand, Japanese Patent Application KOKAI No. 2-78630 discloses that a proteoglycan having an antitumor activity was isolated from the extract residue of the Agaricus blazei Murill fruit body with hot water. More specifically, it is reported that the Agaricus blazei Murill fruit body was extracted with hot water to remove water-soluble components, the resulting residue was further extracted with hot 1% ammonium oxalate aqueous solution; then the extract residue gave the proteoglycan having an antitumor activity.
The substances mentioned above are obtained either from the components soluble in an aqueous medium or soluble in hot water, or from the extract residue with hot water. Thus these substances are all derived from the components insoluble in hot 1% ammonium oxalate aqueous solution.
On the other hand, the present inventors found that a substance having an antitumor activity was obtained from the extract residue of the Agaricus blazei Murill fruit body with hot water followed by further extraction with hot 1% ammonium oxalate aqueous solution. Japanese Patent Application No. 4-160924 (Japanese Patent KOKAI (Laid-Open) No. 6-9423) is directed to the substance.
However, this substance is not satisfactory for the treatment of solid tumor since its antitumor activity is not sufficiently potent.
Either the above substance obtained from the components of the Agaricus blazei Murill fruit body soluble in an aqueous medium or soluble in hot water or the substance insoluble in hot 1% ammonium oxalate aqueous solution which is obtained from the extract residue with hot water is yet insufficient in their antitumor activity.